Self-injuring behavior (SIB) surprisingly prevalent among neurodevelopmentally delayed and mentally retarded individuals, has no known cause and no agreed upon treatment. Expression of SIB may persist throughout the lifespan and into later stages of life, with little change in frequency or quality. Two distinct patterns of SIB have been proposed. One pattern consists of short bouts that may be maintained by environmental contingencies. A second pattern involves protracted periods of SIB that probably is motivated by biological factors. Recent studies from our laboratory indicated that self-injuring behavior was predicted best (and in some cases only) by its own recent history. In a significant majority of individuals, SIB episodes were self-perpetuating and not related to antecedent conditions. We report in this application that individuals exhibiting "contagious" (i.e. sequentially dependent) patterns of SIB also have a disregulated hypothalamic- pituitary-adrenal (HPA) stress axis. We have concluded that there is both a biological predisposition to, and a biological consequence for, the maintenance of SIB. These conclusions may be premature and a more extensive evaluation of the environmental context is warranted. Moreover, there are no data about what initiates a contagious cycle. The purpose of this proposal is to examine the behavioral, environmental and biological circumstances that initiate and maintain SIB episodes. Thirty individuals exhibiting SIB and thirty control subjects, all residing in a large residential facility will be observed in vivo and during an experimental functional analysis of behavior (FAB). Their behavior, interactions and the environmental conditions will be recorded with computer-assisted procedures. Blood will be collected for measures of HPA activity in the morning on a separate day. The Specific Aims are: (i) Determine how the patterns of SIB are affected by environmental context in both in vivo and FAB conditions using sequentially- and temporally-dependent time series analysis, (ii) Determine if there are consistent patterns of environmental events or relations among behaviors that are antecedent to the first or isolated SIB episodes;(Hi)Determine the relation between the HPA stress axis the initiation of SIB, (iv) Apply and evaluate a rational pharmacological treatment to a selected cohort of subjects who present clear evidence of biological (or internal) motivation for SIB. Findings from this project will contribute to the understanding of the emergence and maintenance of SIB.